This invention is directed to a method and apparatus for controlling fiber or filament distribution and orientation in the manufacture of nonwoven fabrics, including spunbond nonwovens, as well as to the resulting nonwovens having a desired fiber or filament distribution and orientation. More particularly, this invention is directed to a controlled application of an electrostatic field in combination with specific target electrode deflection means acting on fibers or filaments prior to deposition on a forming wire or other web forming means. The design of the deflector means located below fiber drawing means, when combined with the controlled application of electrostatics provides separation of the fibers or filaments and directional distribution on the forming surface to result in webs with desired preferential orientation and resulting web properties. The invention also includes a method of producing spunbond and other nonwoven fabrics that can be tailored to achieve a wide variety of physical and other properties for numerous applications in personal care, health care, protective apparel and industrial products.
Nonwoven fabrics or webs constitute all or part of numerous commercial products such as adult incontinence products, sanitary napkins, disposable diapers and hospital gowns. Nonwoven fabrics or webs have a physical structure of individual fibers, strands or threads which are interlaid, but not in a regular, identifiable manner as in a knitted or woven fabric. The fibers may be continuous or discontinuous, and are frequently produced from thermoplastic polymer or copolymer resins from the general classes of polyolefins, polyesters and polyamides, as well as numerous other polymers. Blends of polymers or conjugate multicomponent fibers may also be employed. Methods and apparatus for forming fibers and producing a nonwoven web from synthetic fibers are well known, common techniques and include meltblowing, spunbonding and carding. Nonwoven fabrics may be used individually or in composite materials as in a spunbond/meltblown (SM) laminate or a three-layered spunbond/meltblown/spunbond (SMS) fabric. They may also be used in conjunction with films and may be bonded, embossed, treated or colored. Colors may be achieved by the addition of an appropriate pigment to the polymeric resin. In addition to pigments, other additives may be utilized to impart specific properties to a fabric, such as in the addition of a fire retardant to impart flame resistance or the use of inorganic particulate matter to improve porosity. Because they are made from polymer resins such as polyolefins, nonwoven fabrics are usually extremely hydrophobic. In order to make these materials wettable, surfactants can be added internally or externally. Furthermore, additives such as wood pulp or fluff can be incorporated into the web to provide increased absorbency and decreased web density. Such additives are well known in the art. Bonding of nonwoven fabrics can be accomplished by a variety of methods typically based on heat and/or pressure, such as through air bonding and thermal point bonding. Ultrasonic bonding, hydroentangling and stitchbonding may also be used. There exist numerous bonding and embossing patterns that can be selected for texture, physical properties and appearance. Qualities such as strength, softness, elasticity, absorbency, flexibility and breathability are readily controlled in making nonwovens. However, certain properties must often be balanced against others. An example would be an attempt to lower costs by decreasing fabric basis weight while maintaining reasonable strength. Nonwoven fabrics can be made to feel cloth-like or plastic-like as desired. The average basis weight of nonwoven fabrics for most applications is generally between 5 grams per square meter and 300 grams per square meter, depending on the desired end use of the material. Nonwoven fabrics have been used in the manufacture of personal care products such as disposable infant diapers, children""s training pants, feminine pads and incontinence garments. Nonwoven fabrics are particularly useful in the realm of such disposable absorbent products because it is possible to produce them with desirable cloth-like aesthetics at a low cost. Nonwoven personal care products have had wide consumer acceptance. The elastic properties of some nonwoven fabrics have allowed them to be used in form-fitting garments, and their flexibility enables the wearer to move in a normal, unrestricted manner. The SM and SMS laminate materials combine the qualities of strength, vapor permeability and barrier properties; such fabrics have proven ideal in the area of protective apparel. Sterilization wrap and surgical gowns made from such laminates are widely used because they are medically effective, comfortable and their cloth-like appearance familiarizes patients to a potentially alienating environment. Other industrial applications for such nonwovens include wipers, sorbents for oil and the like, filtration, and covers for automobiles and boats, just to name a few.
It is widely recognized that properties relating to strength and barrier of nonwoven fabrics are a function of the uniformity and directionality of the fibers or filaments in the web. Various attempts have been made to distribute the fibers or filaments within the web in a controlled manner. These attempts have included the use of electrostatics to impart a charge to the fibers or filaments, the use of spreader devices to direct the fibers or filaments, the use of deflector means for the same purpose, and reorienting the fiber forming means. However, it remains desired to achieve still further capability to gain this control in a way that is consistent with costs dictated by the disposable applications for many of these nonwovens.
The present invention includes the use of electrostatics in combination with a segmented target electrode deflector plate below the fiber drawing means acting on fibers or filaments prior to laydown on a forming surface to control the distribution and orientation of the fibers or filaments in the resulting web. Particularly when used in a spunbond process, the resulting web can be made to achieve widely varying degrees of physical and barrier properties, including a very high degree of uniformity if desired. The invention is applicable to spinning a wide variety of polymers in monocomponent, biconstituent or conjugate filaments and using many different bonding steps, such as patterned thermal or ultrasonic bonding as well as adhesive bonding. Also, the filaments or fibers may vary widely in denier, cross-sectional shape and the like and may be combined as mixtures of the foregoing. Single layer nonwoven webs or multilayer laminates may be formed in accordance with the invention.
The invention provides a process for forming a nonwoven web includes the steps of:
a. providing a source of fibers and/or filaments;
b. subjecting the fibers and/or filaments to an electrostatic charge;
c. directing the fibers and/or filaments to a deflector device while under the influence of the electrostatic charge; and
d. collecting the fibers and/or filaments on a forming surface to form a nonwoven web.
In one embodiment the fibers and/or filaments are provided by melt spinning. In a further aspect the meltspun filaments may be continuous and subjected to pneumatic draw forces in a fiber draw unit prior to being subjected to said electrostatic charge. In a specific embodiment the deflector device includes a series of teeth separated by a distance determined by the desired orientation of the fibers and/or filaments in the nonwoven web. Also, in one aspect the teeth are oriented at an angle with respect to the directed fibers and/or filaments, the angle determined by the desired orientation of the fibers and/or filaments in the nonwoven web. The invention also includes the apparatus and resulting nonwoven webs.